Grinding workhead



1, 1964 G. H. LOCKWOOD Dec.

GRINDING WORKHEAD Filed Dec. 3, 1962 FIG.

m m C 0 L H M 0 E G IN VENTOR ration of Delaware Filed Dec. 3, 1962, Ser. No. 241,989 9 Qlaims. (til. 51-256) This invention relates to a grinding workhead and, more particularly, to apparatus arranged to finish a surface of revolution of an annular workpiece by the abrasion method. 7 p I In the grinding of annular workpieces and, particularly, in the the internal grinding of bores, it is necessary to hold the workpiece in a fixed, known position relative to the remainder of the grinding machine. At the same time, it is necessary to provide a holding means intoWhJch 1t is possible readily to remove old workpieces and introduce new ones. The requirements become diificult to satisfy in the case of small workpieces of the type represented by the races of miniature ball bearings. The apparatus used for this purpose in the past has been rather intricate and expensive. Furthermore, because of their complexity they have been readily disabled, so that the machine does not operate properly. The economic disadvantages of permitting an expensive grinding machine to be out of operation for even a short length of time are obvious. These and other difiiculties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the present invention to provide a grinding workhead having a simple,

inexpensive means of holding small annular workpieces and-permitting the replacement of a finished workpiece by an unfinished workpiece with a minimum of difficulty.

Another object of this invention is the provision of a grinding workhead having a'novel means for holding the workpiece and permitting rapid unloading and load- A further object of the present invention is the provision of a grinding workhead in which the workpiece is securely held in a pre-determined position but may be readily rotated ata desired speed relative to the speed of rotation of the abrasive wheel.

It is another object ofthe instant invention to provide 3,158,976 Patented Dec. 1, 1964;

ice

stood that the workpiece shown inthe drawings and all of the parts associated therewith are much larger than would be the actual situation. This is done for the purpose of clarity of illustration. I

Mounted on the workhead 11 is a chute 18 containing unfinished workpieces. The shoe 12 is bolted to the work- 1 22 which extends at a right angle to the upper edge 19.

This surface may be provided with a hardened metal insert 23 preferably formed of a high-friction, hard material such as tungsten carbide.

The disk 13 is perfectly circular and is keyed to a shaft 24 extending through the workhead 11 and provided with a drive pulley 25. This pulley is driven in a wellknown manner to provide for rotation ofthe disk 13 in such a way that, at its point of contact with the workpiece, its peripheral surface moves in a direction away from the shoe 12.

A support arm 26 is mounted on theworkhead 11 for rotation about a pivot 27 and a spring 28 extends between the arm 26 and the workhead to produce a spring bias of the arm toward the vicinity of the workpiece. Mounted on the end of the arm overlying the workpiece area is a guide member 29 having a formed edge 31 which is shown in the preferred embodiment .as a segment of a circle having a radius center of curvature located on an I imaginary line extending between the center .of the worka grinding workhead of relatively simple and inexpensive r a construction.

With these and other objects in view, as will be apparent to, those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

machine embodying the principles of the present invention, and I FIG. 2 is a sectional view of the invention taken on the line IIII of FIG. 1. i

The grinding machine, indicated generally by'th'e reference numeral 10, is shown as consisting of a workhead 11 on which are mounted a shoe 12,a disk 13, and a pressure member 14. A workpiece 15 is shown as held between the shoe 12 the disk 13, and the pressure member 14, while an abrasive wheel 16 mounted on a spindle 17 is shown finishing the internal bore of the workpiece.

. The workpiece is shown as an annular member similar to the outer race of a ball bearing. The grinding machine 10'is similar to that showninthe application. of

Townsend et al., Serial Number 158,974, filed December 13, 1961; it is particularly intended for use in grinding the races of miniature ball bearings, and it will be underpiece 15 and the portion of the workpiece contacted by the pressure member 14. A bore -32 extends through the guide member in line with the radius of the edge 31. Slidably mounted in this'bore is the pressure member 14 which, for the purposes of illustration, .is shown as being in the form of a rod and made of a low-, friction elastomer material, such as a polymer of tetrafluoroethylene, commonly known as Teflon. A set screw 33 is threaded in the outer end of the bore 32 to provide for adjustment of the pressure member with wear.

' Extending through the workhead 11 is a bore 34 intended to provide room for the abrasive wheel 16 to move through the workpiece and also to provide .for the introduction of a gauge (not shown) into the workpiece on occasion. Surrounding the edge of the bore 3.4 where it contacts one end of the workpiece is an inlaidannular insert 35 formed of tungsten carbide. The bore 34 is larger than the bore of the workpiece evenin its finished condition. Also bolted to the Workheadis an outboard platen 36 which engages one end of the workpiece to hold it in place and. is provided with a bore, 37 to permit the introduction of the wheel without interference.

The operation of the invention will now be readily understood in view of the above description. An unfinished workpiece in the chute 18 will drop onto the upper edge 19 of thechute 12 when the pusher 21 is in the right-hand position. Then, when the pusher moves to the left, it will press the unfinished workpiece along the upper edge '19 until it contacts the formed edge 31 of the guide member 29. Further movement by the pusher 21 will cam the guide member 29 and the support arm 26 upwardly against the pressure of the spring 28. This action will lift the pressure member 14 from contact with the finished workpiece 15 and further movement will cause the new, unfinished workpiece to press the old, finished workpiece away from the contact'surface 22 of the shoe 12. The abrasive wheel 16, of course, is withdrawn at this time in the usual manner. The finished workpiece will roll over the edge of the disc 13, being assisted in this motion by the movement of its periphery. The new workpiece will drop over the corner formed by the upper edge 19 of thes shoe 12 and the contact surface 22 and will drop into place so that it contacts the edge 22, the peripheral edge of the disc 13, and the pressure member 14. In the preferred embodiment, the engagement of the contact surface 22 with the workpiece will be at the portion known as three oclock. The peripheral edge of the disc 13 will also contact the workpiece at a position removed'by 120 from the position of contact by the shoe 12, this position being approximately seven oclock. The pressure member 14 will engage the outer surface of the workpiece at a position 120 removed from the other positions of contact in an area known as eleven oclock. Although the contact surface 22 is shown as a plane surface which, theoretically, will engage the workpiece with line contact, it will be understood that a curved contact surface may well be used. Since the nature of the pressure member 14 is such as to wear relatively easily (at least as compared with tungsten carbide) the contact of the pressure member with the workpiece will probably be a cylindrical area.

It can be seen, then, that the position of the workpiece is determined very definitely by the hardened contact surface 22 of the shoe 12. As a matter of fact, when the abrasive wheel 16 is introduced and is fed into grinding contact with the surface of the bore, it does so on a radial line with the point of contact of the outside surface of the workpiece with the contact surface 22. This permits workpieces to be readily reproduced in the grinding machine, so that successive workpieces will be exactly the same size. The driving of the workpiece takes place by the frictional contact between the cylindrical pe ripheral surface of the disc 13 and the outer surface of the workpiece. The pressure member 14 maintains the workpiece securely pressed against the two members, the shoe 12 serving to locate the workpiece and the disc 13 serving to drive it. However, because of the selection of materials, the low friction characteristics of the pressure member 14 assures that it does not slow down the rotation of the workpiece, it being understood that, in grinding practice, it is necessary for the workpiece to rotate. The speed of its inner peripheral surface is, of course, not as fast as the peripheral surface speed of the wheel 16, but nevertheless, it is necessary that the workpiece be rotated. Although the surface 22 of the shoe 12 is hard and presents a good surface for locating the workpiece, its high frictional characteristics prevent the workpiece from rotating too fast. A proper balance of friction between the driving surface of the disk 13, the retarding and locating surface of the shoe 12, and the pressure surface of the pressure member 14 is desirable, and has been suitably provided by the present invention.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to theexact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent, is: r

1. A grinding workhead for use in finishing a surface of revolution of an annular workpiece, comprising (a) a workhead base, 7 V

(b) a shoe fastened to the workhead and having a fixed surface adapted to contact a first portion of the outer surface of the workpiece,

(c) a disc mounted on the workhead base for rotation about a fixed axis and driven to present a moving peripheral surface adapted to contact the outer surface of the workpiece at a position substantially spaced from the said first portion, the periphery of the disc at the position where it contacts the workpiece traveling in the direction away from the shoe, and

' (d) a pressure member having a friction portion which, during grinding, is fixed relative to the workhead base and mounted on the workhead base for movement toward and away from the shoe and the disc, the pressure member being adapted to contact a second portion of the outer surface of the workpiece located in such a position relative to the said first portion and the said position that the workpiece is firmly held in place, the said friction portion resisting rotation of the workpiece to produce a differential speed between the workpiece and the wheel.

2. A grinding workhead as recited in claim 1, wherein the shoe is formed of a very hard, high-friction material.

3. A grinding workhead as recited in claim 1, wherein the shoe is formed of tungsten carbide.

4. A. grinding workhead as recited in claim 1', wherein the pressure member is formed of a low-friction elastomer material.

5. A grinding workhead as recited in claim 1, wherein the pressure member is formed of a polymer of tetrafluoroethylene.

6. A grinding workhead as recited in claim 1, wherein the disc is driven so that its peripheral surface at the said position moves in a direction away from the said I shoe.

7. A grinding workhead as recited in claim 1, wherein the pressure member is carried by a support arm which is pivotally mounted on the workhead and is spring-biased to press the pressure member toward the workpiece.

8. A grinding workhead as recited in claim 7, wherein the support arm is provided with a guide portion having a shaped surface extending on either side of the pressure member to guide successive workpieces in and out of working position.

9. A grinding workhead as recited in claim 8, wherein the pressure member is in the form of a rod and lies in a bore extending into the guide portion in a direction radial of the workpiece.

References fitted in the file of this patent UNITED STATES PATENTS 

1. A GRINDING WORKHEAD FOR USE IN FINISHING A SURFACE OF REVOLUTION OF AN ANNULAR WORKPIECE, COMPRISING (A) A WORKHEAD BASE, (B) A SHOE FASTENED TO THE WORKHEAD AND HAVING A FIXED SURFACE ADAPTED TO CONTACT A FIRST PORTION OF THE OUTER SURFACE OF THE WORKPIECE, (C) A DISC MOUNTED ON THE WORKHEAD BASE FOR ROTATION ABOUT A FIXED AXIS AND DRIVEN TO PRESENT A MOVING PERIPHERAL SURFACE ADAPTED TO CONTACT THE OUTER SURFACE OF THE WORKPIECE AT A POSITION SUBSTANTIALLY SPACED FROM THE SAID FIRST PORTION, THE PERIPHERY OF THE DISC AT THE POSITION WHERE IT CONTACTS THE WORKPIECE TRAVELING IN THE DIRECTION AWAY FROM THE SHOE, AND (D) A PRESSURE MEMBER HAVING A FRICTION PORTION WHICH, DURING GRINDING, IS FIXED RELATIVE TO THE WORKHEAD BASE AND MOUNTED ON THE WORKHEAD BASE FOR MOVEMENT TOWARD AND AWAY FROM THE SHOE AND DISC, THE PRESSURE MEMBER BEING ADAPTED TO CONTACT A SECOND PORTION OF THE OUTER SURFACE OF THE WORKPIECE LOCATED IN SUCH A POSITION RELATIVE TO THE SAID FIRST PORTION AND THE SAID POSITION THAT THE WORKPIECE IS FIRMLY HELD IN PLACE, THE SAID FRICTION PORTION RESISTING ROTATION OF THE WORKPIECE TO PRODUCE A DIFFERENTIAL SPEED BETWEEN THE WORKPIECE AND THE WHEEL. 